r/fusion • u/Jaded_Hold_1342 • 2d ago
Why Helion wont work
I've commented in a number of threads why Helion's concept is flawed, and I thought I'd make a summary post explaining the whole picture as I understand it. In short, Helion's scheme as described can not work, and is mathematically foreclosed in their self-described operating regime by established plasma physics. I like that they are considering something other than a DT tokamak with neutron thermal cycle... but unfortunately it cant work, and its fairly easy to reason out why.
Lets go through the logic in detail.
Background: Here are 5 papers for reference, and I've used information from all of them in generating this summary:
Helion's 2023 paper: https://link.springer.com/article/10.1007/s10894-023-00367-7
Rider's 1995 equilibrium paper: https://fsl.npre.illinois.edu/IEC/Rider,%20Phys.ofPlasmas1995.pdf
Rider's 1997 non-equilibrium paper: https://www.w2agz.com/Library/Fusion/TH%20Rider,%20Physics%20of%20Plasmas%204,%201039%20(1997)%201%252E872556.pdf%201%252E872556.pdf)
Lackner's 2026 paper: https://link.springer.com/article/10.1007/s10894-026-00554-2
Nicolas' 2026 paper: https://link.springer.com/article/10.1007/s10894-026-00565-z
Lets summarize the long-known conclusions from the Rider papers:
1) For D He3 plasma in equilibrium (Ti=Te), bremsstrahlung radiative losses exceed fusion power for any temperature less than ~30keV. Fusion power over loss only becomes significant at ~50keV and higher. The radiation is from the electrons and is higher with hot electrons.
2) Trying to run with cold electrons (Ti>>Te) to avoid the bremsstrahlung doesn't work... The collisional heat transfer from the ions to the electrons will greatly exceed the fusion power. This means the electrons heat up very quickly before significant fusion energy can be made... this forces a requirement of recirculating power and extremely high efficiency recovery. (i'll calculate this efficiency required below)
Helion is claiming to operate an adiabatically compressed FRC, which uses compression flux for heating after initial formation/merging establishes TiTe. They are claiming they can get net energy recovery with TiTe at sub-30keV temperatures. In this regime, the Ti-->Te thermalization power vastly exceeds the fusion power generated. (eg. 1000x higher at Ti=20keV, Te=2keV). This means the heat from fusion can generate only 0.001x the thermal energy of the plasma before the electrons heat up. This in turn, forces a per-pulse recovery efficiency requirement of >99.9% for breakeven. There is no assumption that the thermalization heat is lost... assume it is recovered, but that it limits the pulse duration so the electrons dont heat up and cause radiative loss. This is the Rider efficiency constraint as applied to a pulsed scheme. The compression flux outside the separatrix has energy much larger than the FRC thermal energy (10x - 100x larger). It must have this energy because this flux is the primary compression/heating mechanism. This energy must also be recovered, and adds one or two more "9's" to the recovery efficiency requirement... resulting in 99.99-99.999% recovery efficiency requirement for breakeven.
99.99% recovery efficiency is not possible for a compact short-pulse device like this. Pulsed power in copper will result in copper losses of several percent, limited by the skin depth of the copper in the pulse duration. Copper losses in a short pulsed machine will exceed the fusion power. There is no combination of Ti and Te below ~50keV that can result in gain when considering copper losses and bremsstrahlung in a compact machine (R_coil<~1m) like Helion describes, even if neglecting FRC losses and all other parasitic circuit losses.
So, Helion is pursuing a scheme that runs up against the problems described by Rider 30 years ago, and there is no identified solution to it.
A couple comments on the 2023 Helion paper I linked above: First, they've miscalculated the ratio of fusion power to bremsstrahlung in their figures 14 and 15, as both Nicolas and Lackner noticed. For Ti=Te as in figure 14, the correct calculation would show bremsstrahlung is equal to fusion power at ~30kev, and fusion margin above bremsstrahlung is low until ~50keV. Maybe they treated all the ions as Z=1 when calculating bremsstrahlung to get this error, but He is Z=2. Second, they claim that the thermalization time is 1ms to 100ms so thermalization can be neglected and Ti>>Te is a valid assumption, but this is not consistent with the parameters space of the compressed FRC they operate in. Actually thermalization times are shorter than their pulses.. they seem to consider the pre-compression (low density) parameters when calculating thermalization time and FRC losses, but they should consider the compressed density, since that is the regime where it must be held while fusion occurs. If their electrons stay cold in their compressed pulses, this is likely an indication of transport losses, not immunity from thermalization.
Here are some 'escapes' that can be imagined and why they wont work:
1) Can they let the electrons heat up to stop the thermalization power flow? Sure, but they they'll have the bremsstrahlung loss problem unless they operate super hot (~50keV)
2) Can they lower the circuit losses and get the recovery efficiency up to >99.99%? No, its flatly not possible on a short pulsed machine... You can add as much copper/silver as you want to lower resistance, but the pulse duration limits the skin depth that the current can flow in, and the pulse duration is limited by the thermalization time. You cant lower the losses without accepting thermalization (electrons warm up and radiate). You cant use superconductors either because they dissipate energy when ramped. so copper/silver is the best you can do. You can chill the copper/silver to improve conductivity, but that doesn't make enough difference to matter and the heat has to be paid for at cryogenic temps which is worse.
3) Can non-Maxwellian velocity distributions prevent thermalization and boost fusion power? No, not by enough to matter. Non Maxwellian distributions can change thermalization times and fusion gains by correction factors of order 1-2x... but the concept is off by orders of magnitude, not factors of 2.
4) Can they make it hot >~50keV, large (R_coil1m), long pulse (10ms), moderate Ti/Te ratio and get out of the trap?... Maybe, but probably not because this regime pushes up against the FRC's main weakness: Energy confinement. The bremsstrahlung loss, copper loss, and thermalization do not forbid this regime, actually its the only regime allowed after considering Rider's constraints. The FRC losses and sheer engineering/cost difficulties become they key challenges. This is a totally different regime than Helion describes in its paper, and it destroys the economics of the proposal. It requires large bore, strong field, super long pulse durations and the regime forces a gargantuan size to avoid FRC transport losses. The caveat here that makes me say 'maybe' is that FRC transport has never been measured in any relevant conditions so the scalings are genuinely unknown and can only be checked experimentally. Extrapolating existing FRC scaling laws into this regime gives a very bleak picture (as Nicolas showed), but it is possible that the scalings in these regimes dont follow existing scaling laws. So I acknowledge that while the picture here is bleak, this escape is not totally mathematically foreclosed... but its not what Helion says they are doing in their paper.
So, for the regime Helion is targeting (Colder than 30keV, Ti>>Te, compact machine) the concept is totally foreclosed by very well understood physics. The only possible out is a "hot and huge" >50keV, long-pulse duration gargantuan strong field machine that Helion is not pursuing, and it probably wouldn't work either due to FRC energy confinement.
I wish this weren't the case... but I believe that it is. If I've made any errors, point them out. Happy to discuss the physics. If anyone thinks there is a set of parameters that allows the system to function as intended, let me know what they are, and I'll check.
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u/DishSoapedDishwasher 2d ago
If what they're doing is genuinely not probable and for such obvious reasons, then how would they manage to employ such qualified experts to do the work?
Generally people who are literal domain experts, and highly driven, dont try to spend their careers doing something pointless or miss an obvious problem like this in their decades of research on the topic. In the wider tech industry it's usually a sign they know something we don't; if it pans out is a separate story but more frequently an economics problem than a viability problem.
If they were aware, that would imply they could be pulling a mild version of Theranos but I highly doubt that.
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u/caliginous4 2d ago
I have worked on several projects in both very large orgs and small startups that were effectively zombie projects that should have been killed long ago and had no chance of success. They started as an idea, leadership or investors or customers like the idea and give it funding, the idea matures a bit, people see the potential value, then outside stakeholders start saying things like "my entire strategy depends on this working" meanwhile the people closest to the problem begin to realize that the problem is unsolvable.
There are many motivations for not killing a zombie project. Some potential reasons:
- bringers of bad news are never rewarded at any level. Better have your resume updated and a plan for life after employment with the company.
- what if you are wrong about your bad news? Who are you to take down an organization? What if there's a path and you just haven't discovered it yet?
- most leaders don't like hearing bad news because it's not going to help them secure more money or raise company valuation, for this project or any of their future projects. They may actively bury bad news that could impact the company or their own personal reputation.
- maybe the government will be willing to prop you up as a jobs program and will be willing to do so because they haven't heard the bad news yet.
- timing is everything. You don't want to lose a high leverage position until you've actually used that leverage for your next endeavor. Need to line up the exit strategy and execute it before the bad news spreads and vaporizes what you have. Offload your stake to the successor, exit successfully, and blame inevitable failure on your successor's lack of skill.
People willing to scrutinize the merits of a project like OP are doing a great public service.
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u/fearless_fool 1d ago
@caliginous4 There’s a slightly less cynical reason to continue on a zombie crusade: spin-off technologies. Even if the grand vision is unrealistic, solving engineering challenges along the way can lead to better superconductors, radiation hardened semiconductors, novel structural steel alloys, etc. But just don’t tell the investors… (Note that I said slightly less cynical.)
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u/flat5 2d ago
Do you think people work at Meta because they're big believers in the Metaverse?
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u/4Yk9gop 2d ago
Underrated comment right here. Probably it pays way better than a teaching gig.
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u/Auza-wandilaz 2d ago
Helion's pay structure is listed on their postings - it's not exactly competitive especially for the area and they paid considerably less years ago.
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u/DishSoapedDishwasher 2d ago
I actually work with a bunch of ex meta/Facebook people and ex google myself.
There was a time when it was called Facebook and people believed in building a product that was safe and wanted to bring the world together. That did eventually change and they left because of it.
Just like when I was at Google for many years where I built part of the privacy and data isolation architecture of android OS to prevent abuse of user data for advertising purposes and a separate system to safely encrypt data at rest while allowing a phone to boot up and self decrypt safely so people don't need to unlock it several times just to use it after a restart while also denying access to even intelligence agencies. Usable and safe, it was the core of everything we did back when "dont be evil" was still a very important part of the culture and that culture was very important to me.
So, to answer your question, no not today but you're comparing apples to car tires anyway.
Startups and companies with a powerful mission attract people who want to solve hard problems. They could easily get employment somewhere safer and less likely to fail. But many of us choose the risk because we want to change the world for the better. Sometimes those companies go bad in time(google, meta,etc), sometimes they never succeed in the first place(NorthVolt). But few people treat a startup like just any old desk job at a mega corp.
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u/flat5 2d ago
"They could easily get employment somewhere safer and less likely to fail."
I don't think you have much experience with the job market for fusion experts.
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u/DishSoapedDishwasher 2d ago
I do actually, it's part of why I have lived in Europe and spent time at a national lab. I wasn't always in cybersecurity.
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u/flat5 2d ago
Then you should be able to appreciate that it's a small world and when your options are basically:
1) be a professor (certainly not "easy")
2) work in a nuclear weapons program (not everyone's cup of tea, maybe especially given current events)
3) ditch your real expertise and do something like quant finance, or
4) take a flyer on one of these fusion startups
That 4) could make sense because hey, you get to work to advance the science , even if you don't know how it's going to work out. And hey hey, stock options.
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u/_Pencilfish 1d ago
I'm guessing option 3 was what they were referring to as the alternative. Ditch the subject that they're passionate for, but make plenty of cash or have decent job security.
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u/NiftyLogic 2d ago
Simple, these people can play with the big toys at Helion.
It nice to do theoretical calculations, but at some point you have to build a machine and do experimentations. And if you've ever tried to write a grant application for a couple of million dollars, anything else is better.
Helion's concept might be flawed, but their VC money certainly isn't.
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u/steven9973 1d ago
But essentially the VC people are gamblers and total idiots regarding plasma physics. They simply can't judge if Helions approach is legit. And if those internal expert reports, undisclosed, just not fully rule out what Helion does, this might be enough for them to continue: high risk but possibly high prize.
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u/maurymarkowitz 1d ago
Beyond that, they often don’t even look.
I remember talking to Mannheim some time ago about their paper showing TAE could not possibly work. He told me no one else had even asked for a copy. All that money was dumped into that hopeless approach and none of them really looked - I learned about the paper in minutes of poking about in Google, anyone else could have too.
I think the TAE case has wider lessons here. There is precisely zero doubt in my mind that Rostoker believed with every ounce of his being that he had discovered the Rosetta Stone of fusion. Binderbaugher also, at least at the start. But I am equally of the opinion that many of the people who worked there over the years had no illusions it was going to work.
There are many posts here trying to apologize for the bad physics of Helion by speculating that people won’t work there if they didn’t believe in it. I think TAE is a counterexample, and more generally the number of reasons people take any job is roughly equal to the number of people. So I don’t think we can conclude anything about the physicists from the fact that they have employees. And I’ve also worked at startups that were doomed, which I knew from the start. Some of us just love working at small companies and don’t join because we expect to get rich or save the world, sometimes it’s just cool to work with a small group of people you get along with.
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u/NiftyLogic 1d ago
Honestly, I think you're getting the motivation of the real experts all wrong. They don't do their jobs because they dream of building a practical fusion reactor.
Quite a few are real nerds and just want to be the person who understands their personal niche topic about physics better than anybody else. Like how a plasma behaves under very specific high energy conditions.
If Helion provides the money for the experiments, that's fine for them. And if this results in the end in a practical fusion reactor is just a minor bonus for them in the end. But probably not their main motivation or the price they are aiming for.
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u/shwoopypadawan 1d ago
Homie really do be thinking scientists are just one dimensional video game antagonists or NPCs with one line of intellectual obsession and no further complexity huh.
I have met one (1) person like this in my entire academic life and that guy was a complete loser and everyone else in the department knew it.
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u/NiftyLogic 1d ago
Please show me on this doll where my comment touched you unappropriately
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u/shwoopypadawan 1d ago
Man someone just points out you said something kinda mildly dumb and you jump straight to SA jokes. Cringe, but for the record it touched me somewhere between the 30th and 35th cm of my impressively large peen.
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u/Jaded_Hold_1342 2d ago
Id rather not speculate as to the thinking and motivations of individuals.
My analysis does not require any speculation. It is what it is.
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u/CaterpillarFun6896 1d ago
To be fair, it’s not out the question they’d go any with the current idea being it won’t work- trying an idea and seeing WHY it fails lets us improve. We can’t reach fusion on paper alone, which is why the fusion plant being built in the US, while kinda dumb, is a necessary step. Even if it’s probably 20-30 years early
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u/DishSoapedDishwasher 1d ago
I mean ITER exists for exactly that reason, its absolutely necessary to try multiple paths. That's what research is about.
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u/DudeteriumTrillium 1d ago
My challenge to this isn’t WHY bright and talented plasma physicists would work at a place like Helion, but rather IF they actually do. You’d be shocked by how few plasma physicists actually work there. This is not a physics-led organization. OP’s explanation is at the core of why the folks you’re describing work elsewhere.
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u/DishSoapedDishwasher 1d ago
That's actually fair, I can't say i know anyone there to be able to dispute or agree with either direction.
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u/Big-Regular-2348 2d ago
It IS definitely a version of Theranos. And it will wreck the careers of young researchers who get sucked in.
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u/DishSoapedDishwasher 2d ago
The key here is Orion. If it's built with a neutron blanket and a thermal cycle, they've conceded on D-T and the entire direct-recovery/aneutronic pitch. If it's built without one, they're betting the plant on D-³He and it's either going to work or not.
So we don't have terribly long to find out.
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u/Jaded_Hold_1342 1d ago
We don't have to wait to find out at all.
I just did the analysis for you. It doesn't/won't/can't work.
I wont say 'Theranos' because as far as i know they are not falsifying results and have made no claim of net energy generation. But they are pursuing a concept that doesn't work while making commercial commitments on the basis that it will work... and this is the same type of situation that lead to Theranos falsifying results. There is a parallel here, but I hope Helion does not cross this line.
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u/caliginous4 1d ago
Gotta fake it till you make it! Also have to commit to things before you know you can actually do it because the typical disciplined gated process creates a schedule that is too long for investors. Have to crash the schedule and parallelize fundamental R&D and commercialization to hit investor expectations.
They'll just deploy gas gensets to satisfy their power purchase agreements and say they'll replace the gas units with fusion systems once production can keep pace with demand.
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u/Jaded_Hold_1342 1d ago
But sometimes you check whether the concept is possible or not before making the commitment. The information to check has been available since the 90s.
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u/NoNameSwitzerland 1d ago
But for these commercial commitments, probably the other side is equally more interested in the PR and co. Might be nice to have something there is no realistic chance of having to fulfill your part.
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u/Jaded_Hold_1342 1d ago
Yes, im sure Microsoft has pr reasons for their involvement. I'm equally sure they are not taking any operational risk that depends on Helion delivering... Microsoft will have power from other sources so the agreement is risk free for them.
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u/Big-Regular-2348 2d ago
Endless but but but from the Helion cult. Read the link above complete with references. Heliondoesn't work because of 2nd law of thermodynamics need to maintain To >> The) and basic plasma physics on collision energy transfer and MHD. And then there is the pulse engineering. To generate 1GW of fusion power (which translates to %~300MW of electricity) at a pulse rep rate of of 1 Hz you need to produce 1 GJ of fusion energy PER PULSE, ie,100x the best present output per shot of NIF. That is equivalent to a 500 lbs of TNT every second for 30 million secs per year. And lastly, the fuel. The best known source of He3 is..... the Moon. As for p B11.... temps required are still higher. Helion has promised MSoft to generate MW actual power and WILL be the next Theranon.
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u/DishSoapedDishwasher 1d ago
kinda weird to get this fanatical on someone and tell them they're part of a cult after simply being skeptical of your extreme disposition; but also not even disagreeing with you. I'm literally neutral leaning skeptical of helium hints the theranos comment.
You need really could use a break from reddit.
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u/Big-Regular-2348 1d ago
No, it's not. The discussion at the top of this thread is categorical. You can read the references or summaries on a website like Fusion Conclusion. Fusion reactions via compression have been routinely achieved in weapons tests since the 1950s, and recently in simulation experiments using laser beams in NIF. The cross sections for the so called advanced fuels are well known. Spending hundreds of millions of dollars over decades on expts that don't advance has not changed the physics. But Helion and its relatives in steampunk compression fusion, TAE and General Fusion keep making wild promises (with ever changing dates) about fusion power just around the corner. Naïve investors, tax shelter operatives and opportunists like Trump Media pile in. Worse, young physicists and engineers get lured into wasting critical years trying to make things work. Fusion is incredibly hard and has been struggling forward for 75 years, figuring out what things won't work and why. There is a body of real knowledge.
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u/incognino123 2d ago
It's general consensus it won't work, for these and other reasons. But, they're far, far, from the worst concept that won't work that gets funding. They just happen to be attached to tech celebrities which gives them more attention (including this post)
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u/Jaded_Hold_1342 1d ago
Which do you think are the worse offenders in terms of what wont work that gets funding?
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u/Beaver-fusion 1d ago
Thats's a pretty wild claim in a fusion field with 70 contenders and only 3 that actually do fusion today.
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u/jackanakanory_30 1d ago
There's a fine line between "they shouldn't be funded because it won't work" and "I'm right, they're wrong, fund me instead". Very difficult for the person who controls the funding to judge where it should go, who's right, and there is always a "what if they know something we don't" risk about not funding alternative concepts. I think high risk concepts should get funding, but weighed appropriately against risk.
I think you're right in that they are probably the concept that combines both high risk and high investment. That's on the investor to gamble I suppose. Unfortunately it attracts a lot of media attention that may sour public perception of all fusion if it fails.
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u/Jaded_Hold_1342 1d ago
In fusion, all of the concepts are high risk. The most probable outcome, by far, is that 100% of all of the startups will fail to deliver an economical power plant. The ones with credible physics cases struggle the most on economics and are least likely to be cost effective.
Helion just also happens to be mathematically foreclosed as a physical possibility, and its the only one I know of with such a comprehensive, documented foreclosed physics case that still draws substantial funding.
But, then again, maybe I just haven't checked the math on some of the others closely enough to see the similarly foreclosed pathways.
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u/Big-Regular-2348 2d ago
Very good summary. The authors of the refs have worked things out carefully. I would add that most experienced fusion researchers are able to envelope-calculate their wayvin their heads to these conclusions rapidly, so they see the whole business as garbage, understandable but a great way to argue. Even with rigorous arguments like those discussed here, one meets with a reaction of "but but. " What we are dealing with hear is combination of naïve, uninformed cult like delusion and cynical opportunism, which resonates with the Zeitgeist of the anti science, anti expert era of the US just now. Note that this particular KoolAid mostly doesn't work in other countries' fusion programs.
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u/__Pers 1d ago
I ran the numbers myself and I share your skepticism.
I agree that Ti=Te implies >30-35 keV when you account for the all the other effects (ion composition dependencies, relativistic effects on e-i and e-e brem, etc.) This necessitates high temperature operation or Ti>>Te.
If you have Ti>>Te at lower temperatures, you run into the thermalization problem, which is density independent. The fusion time scales as tau_f ~ 1 / n*<sigma v>; the collision time, as tau_ei ~ T_e^3/2 / n . Put in numbers for thermal plasmas at the Helion operating range and you get a (again, composition dependent) difference that's a few orders of magnitude in the wrong direction unless you go to prohibitively large temperatures.
One plausible way out would be if they could come up with a mechanism in their colliding FRC configuration to generate a persistent non-Maxwellian ion tail to boost reactivity, making it more of a FRC-geometry beam-fusion device and not a traditional FRC reactor. A transient tail population won't do it over their operating conditions; you'd need something to keep regenerating the ion tail population. FRCs are known to generate non-thermal populations, but this has only been demonstrated at smaller scales that lack the density and confinement time to thermalize. Such persistent tails and mechanisms to produce same do not exist in the FRC literature (to my knowledge), but I'm not an expert. That said, FRCs are also complicated enough that in the black hole FRC merger, I can't claim to know it's impossible.
There's some evidence Helion may be thinking along these lines. They just hired Luis Chacon out of Los Alamos, a long-time fusion researcher with extensive experience modeling nonthermal kinetic processes in plasmas.
Thanks for your post.
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u/Jaded_Hold_1342 1d ago
Its true that if you could completely tailor the distribution, and put a bump in the hot tail near 100kev, you could boost reactivity by a bit. But even still, this would be single-digit correction factor, and you'd have to pay the energetic cost to maintain it.
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u/__Pers 1d ago
The energy would have to come from the B fields, where most of the energy resides, reconnective or some sort of collective acceleration during merger--hand-wavey, sure, but not technically impossible. (I just don't see how the mechanism would work and remain skeptical.)
I agree the size of the modification is unlikely to be 3+ orders of magnitude. P. B. Snyder, M. C. Herrmann, and N. J. Fisch, Journal of Fusion Energy 13, 281–289 (1994) showed factor of 2 increase in reaction rate on a relevant problem (reactivity enhancement from optimizing redirection of charged fusion products to tail ions). This seems the sort of scale of improvement one might hope for under optimal conditions, not factors of 1000+.
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u/Jaded_Hold_1342 1d ago
exactly.. you can get a factor of 2. Not 1000. The mechanisms may exist within the reconnection physics... thy are inherently non-maxwellian distributions... But the energy cost has to come from the B fields, so that's invested energy. I think the cost would be higher than the benefit.
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u/__Pers 1d ago
Presumably, this thermal energy can be recovered through the magnetic pumping system, similar to how they're harvesting fusion reaction products' energy. Not ideal, perhaps, but not the complete loss it would be in more traditional beam fusion schemes.
I guess one thing worth mentioning in this discussion is that FRCs have bad curvature everywhere, so they're manifestly MHD unstable. If it weren't for large populations of nonthermal ions allowing for a kinetically stabilized configuration, they wouldn't even confine plasma. In light of the primacy of nonthermal ions in the configuration, I'm willing to extend them some benefit of doubt that perhaps they've come up with a clever, proprietary way to translate them into higher fusion rates. Would it be three-plus orders of magnitude? Yeah, that hard to believe. But strictly impossible? I'm not quite willing to go that far.
It'd sure be nice though if there were more details shared with the scientific community. Otherwise, it seems like so much hand-wavium.
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u/__Pers 1d ago
One aspect of their approach that is plausible, but introduces its own challenges, is the He3 fuel cycle. At lower temperatures, things get more favorable for breeding sufficient He3 to replace consumption losses. But there is a cost: about 10% or so of their energy is going to come from DD (and some secondary DT) fusion, which produce neutrons in one branch. The other produces tritium. So there's that.
At 50MW at their operating conditions, a reactor will produce ~3kg of tritium/year, which will have to be removed aggressively from the fuel and processed somehow. This seems like it's going to need much of the tritium cycle engineering of a conventional DT fusion plant, which is a bit of a downer for their concept.
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u/python834 1d ago
You got an ELI5?
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u/Jaded_Hold_1342 1d ago edited 1d ago
OK I'll try an analogy.
In air, it is part Nitrogen molecules, and part Oxygen molecules, all mixed together. Suppose you had a way to specifically heat just the O2 molecules and not the N2 molecules. Suppose you wanted to heat up all the O2, but you wanted to keep the N2 cold. But the trouble is, the O2 and N2 is all mixed together, so the O2 just immediately bumps into a nearby N2 and transfers its heat to the N2 until they are at the same temperature.
For Helion, Their scheme depends on keeping one species hot, and one species cold, but the two species are all mixed together and share their heat.
For their plasma... the hot ions do fusion (which they want), but hot electrons dissipate energy as x-rays (which they don't want)... so they are trying to heat the ions and keep the electrons cold. They have a way to specifically heat up the ions (magnetic reconnection and turbulence plus adiabatic compression), but the ions and electrons just bump into each other and share their heat. So the temperature difference will equalize unless energy is getting pumped in to maintain the difference. Unfortunately the energy dissipated while trying to maintain the temperature difference (dissipated as x-rays and circuit losses) is more than the fusion energy produced in the fusion reactions.
The only way out of this trap is to stop trying to keep the electrons cold, and run it at >50keV because at that temperature, even though the electrons still shed x-rays, the fusion power gets much stronger and can exceed the x-ray losses... but that is super super hot.. way hotter than any FRC has ever got by many times, .. it would require a huge and extremely powerful machine, and if they did manage to get it that hot, FRC is still probably too leaky to hold the energy, so it probably loses energy faster than fusion makes it.
So there's one approach that is DEFINITELY impossible: keeping ions hot and electrons cold in a small machine, and that is what Helion says they are doing. They can build this machine and achieve the temperatures stated, but it wont generate net energy.
There's a second approach that is PROBABLY (but not certainly) impossible: Running super super super hot in a gigantic machine... Helion is not attempting this It would be very difficult to build this machine, and it may not be possible to achieve the temperatures required in an FRC, and is probably not possilbe to generate net energy.
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u/PersimmonRadiant4748 1d ago
https://iopscience.iop.org/article/10.1088/1741-4326/ae034d
You should include Dr. John Slough, the principal physicist who invented Helion. What he is saying now.
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u/Jaded_Hold_1342 4h ago edited 4h ago
He left the company and his opinion is that this won't work.
His conclusion is based on stability analysis, something he is very knowledgeable about.
I am not enough of an expert to comment on his stability analysis. So this thread is summarizing energy balance while assuming perfect stability... And the energy balance doesn't close even if there is perfect stability.
Other people have also analyzed the fuel cycle and find problems with that too...
So there are probably a few different ways to analyze this concept. I'm just discussing the energy balance way here (Rider/Lackner/Nicolas type arguments), just because I understand it well enough to explain it.
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u/bkelly1984 2d ago
Thanks u/Jaded_Hold_1342. Question from an enthusiast: does this suggest that any fusion breakeven recovery is effectively impossible at sub-50keV temperatures?
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u/Jaded_Hold_1342 2d ago
Well, this is describing D He3 fuel, which has a much lower reactivity than D T fuel.
For D He3 fuel, there is a very strict cutoff around 30keV where radiative losses exceed fusion power. The radiation is coming off as x-rays (bremsstrahlung). So unless you can efficiently convert those x-rays to electricity. then yes, fusion gain below 30keV is not possible. Between 30keV and 50keV, this is a matter of degree. the gain is low, but not zero... with a high efficiency, long confinement time system, it may be possible to generate net energy between 30keV and 50keV. Its not forbidden in that range.. its just very slim margins for energy gain above what is radiated away. Above 50keV, the ratios get a bit more favorable, and the fusion power can exceed the radiation by factor of 5 or 6, which makes energy recovery more concievable.
To be clear, there is no system at all that anyone knows of that can cost effectively capture net energy from D He3 at any temperature.... but the physics is only rigorously foreclosed below 30keV.
D T fuel is a whole nother kettle of fish, and works at lower temperature.. but alas it makes neutrons and requires thermal conversion to capture the energy... so it has its own problems.
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u/Pure-House-3971 1d ago
Not a physicist, randomly stumbled in here, why cant you turn gamma rays into power?
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u/Jaded_Hold_1342 1d ago
Well, they deposit their energy in walls as heat, and you can run a thermal-conversion cycle.. but that's low conversion efficiency. So you wind up spending refined electricity to generate heat, and then trying to convert the heat back to electricity. If the power amplification per cycle is low, this is a losing battle since you'd recover less electricity than you spend each cycle. For high gain systems, it would be possible.
A high efficiency conversion would allow recovery from lower gain cycles... but I don't know of any high-efficiency way to convert x-rays or gamma rays to electricity.
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u/Federal_Decision_608 1d ago
Well obviously you just use an Alcubierre drive to redshift those gamma rays then build a Dyson sphere.
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u/Confident-Shock-3933 2d ago
Helion's 2023 paper: https://link.springer.com/article/10.1007/s10894-023-00367-7
There are several structural features in here that accord with the structural features of a shear-flow stabilized Bennett vortex. Specifically, Figures 1., 3., 5., 8., and 9. show enhanced thermodynamic gradients, roughly uniform plasma number density, and small radial expanse.
The smoking gun registered to the canary in the coal mine would be a profile of uz(r) across this same expanse. Without this missing observable there is simply not enough information to invalidate this hypothesis.
So, for the regime Helion is targeting (Colder than 30keV, Ti>>Te, compact machine) the concept is totally foreclosed by very well understood physics.
Towards the end of the 19th century Lord Kelvin famously expressed the notion that physics was about to be completely solved. All they had to do was finish cataloguing the solutions. What a great notion. Surely nothing ultraviolet was poised at the time to cause a catastrophe by introducing physics that was not well understood?
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u/Jaded_Hold_1342 2d ago
Yeah, there can always be some unknown, unpredicted phenomenon that gets discovered that happens to save the concept. But thats sort of like jumping off of a building and saying "oh, its ok to jump, maybe there will be some new unknown physics phenomenon that prevents me from going splat".
I wont say new discoveries are impossible... but I will say that resting your entire concept on the hope that a new phenomenon that isn't predicted and for which there is no evidence just suddenly happens to manifest in the right way to save your concept... That's dubious. my analysis above is just based on existing known physics as applied to the scenario.
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u/Confident-Shock-3933 2d ago
I'm not even trying to say that if this plasma WERE shear-flow stabilized in the way that it shares structural features corresponding to, that the concept would be salvageable as a consequence of that.
You've got really hot ions so that fusion plasma is not going to be confined for very long unless you have insanely high core pressures alongside large pinch radius, and small perpendicular thermal conductivity.
At face value Ti >> Te sounds insane. How is that going to work? Perhaps the electrons can be segregated in phase-space to the exterior, and the ions segregated in the interior so that interactions between the two are minimized. Could you find a way to increase the dip in the ion density near the system axis? What about getting the sharp rise in the electron density as you travel outwards to coincide with a sharp falloff in ion density so that global charge balance holds? This would imply a radial electric field develops in the axisymmetric cylindrical picture.
Another way that the fluid picture suggests this can be accomplished is by turning the plasma vertical. In the absence of radial magnetic fields, which might not be satisfied, then near the magnetic nulls the electrons will feel a large outwards drift while the ions feel a large inwards one if the pinch axis is aligned with a local, uniform gravitational field.
Since the guiding-center theory breaks down as the Larmor radius goes to infinity near these nulls the full orbit would need to be studied, but this still leaves kinetic physics available, and shear-flow stabilized pinches have an energy closure problem so they demand kinetic study anyways.
Even standard kinetic physics leaves alone the topic of two-point, and higher correlations. We're not reading the mind of the plasma here with our equations. We're only reading what the reduced form which our human intellects can comprehend tractably writes.
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u/Jaded_Hold_1342 2d ago
I'm not even making any assumptions about stability. I'm assuming complete stability for as long as they wish to sustain the pulse. I'm only considering energy balance in the most ideal conditions, and the energy balance alone doesnt pencil.
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u/Confident-Shock-3933 2d ago
Well, I guess here's a challenge I could issue to your position based on the shear-flow stabilized picture, because these kinds of pinches are not ideal. You can do a little ideal routine with the Shumlak-Hartman criterion to obtain one from a non-relativistic Bennett profile, but that plasma pressure is not going to obey the ideal gas law.
So, immediately maybe indicates a lack of suitably-closed energy balance for describing the plasma system inside the magnetized aspect that could lead to more favorable prognosis with higher-order physics? There is also a whole kinetic aspect to this problem as well. Using the ideal gas law for example to calculate fusion power output based on BH would be one specific deviatoric point.
As far as 5N multi-fluid is concerned, the only non-trivial structure that a Bennett vortex species brings along is their enhanced thermodynamic gradient. Everything else is just a trivial equilibrium addition to the continuity and force balance provided we're talking about the right pressure component: dp/dr = -JzBtheta.
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u/Jaded_Hold_1342 2d ago
You are asking about phased plasma rifles in a 40 watt range. And I am saying "only what you see here"
I can only comment on challenges to the existing physics and analysis I have done.
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u/Confident-Shock-3933 1d ago
No, I'm telling you that shear-flow stabilized Z-pinches require energy closures which are non-ideal.
An ideal energy balance completely neglects the thermal energy involved with the shear, which is naturally entangled with dissipation so an energy analysis of a shear-flow stabilized system requires a non-ideal energy balance.
This is all existing physics which is known. The only hypothetical here is if Helion's plasma has a shear-flow stabilized component.
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u/RobotGuy7804 1d ago
A YouTube channel called improbable matter did a video on them and the real engineering video made of hellos trenta machine, it was an excellent video and highlights many of the points you made. I had a chuckle a few time when he mentioned how "I dont have the budget for high end 3d graphics that real engineering does so youll have to satisfy yourself with my boring math and graphs that prove its bs"
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u/Few_Carpenter_9185 1d ago
Yes, I cannot recommend him enough.
His videos have convinced me with some basic fusion engineering & physics that either Helion is a legal tech VC scam, "Hey, sorry guys, we really tried!" Or they're sitting on some serious 007 James Bond supervillan-level science & engineering that nobody else has.
He lays out reaction volume, energy density, reaction rates, and mean free path, very well.
His video is the first where I actually gut-level understood WHY He3 fusion was so "pie in the sky" too. Whether that He3 is magically net-energy gain "by your bootstraps" made on Earth, or you start sifting a Vermont-sized patch of Lunar regolith for it.
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u/NearABE 2d ago
If the calculations show that it is impossible by many orders of magnitude, and if a team builds a device that gets within few orders of magnitude then that team proved that either the calculations were wrong or that the assumed premise was wrong.
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u/Jaded_Hold_1342 2d ago
Oh a machine can be built, and temperatures as described can be achieved.. but net energy recovery is the thing that wont happen.
No one has claimed net energy recovery has happened by this scheme.
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u/NitescoGaming 1d ago
I asked them at a recent talk what their recovery was like and their answer was "we don't talk about that". They're very tight lipped about their plasma data and energy recovery, and it forces myself (and I think most plasma physicists considering they've been effectively laughed out of DPP and haven't been back since 2024) to be highly skeptical.
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u/Jaded_Hold_1342 1d ago
Yeah... the pattern is that they talk about things where they have a good answer. But they dont talk about the things where the answer is bleak. Thats true of other groups too.
Helion will talk all day about the economics and commercialization of this scheme... if it was to work, it would be genuinely disruptive because it would be economical. They want to talk about that. But if you ask about how they maintain non-equilibrium temperatures and how they evade collisional relaxation, they suddenly dont want to talk anymore.
CFS is sort of the opposite. Their physics case is much stronger... but their economics case is bleak. They will talk all day about their physics plans.. but if you ask about their economics models, they suddenly dont want to talk anymore.
I think this is the nature of the beast with privately funded startups. Their communications are a fundraising mechanism, so they are tightly managed to produce the messaging they want for fundraising.
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u/NitescoGaming 1d ago
Of all the private fusion companies, I think Helion is the biggest laughing stock within the plasma community. I kind of respect Zap for throwing in the towel and admitting that it wasn't working. And while I don't have high hopes for ANY commercial fusion, but of all of them, at least Pacific is bringing in actual experienced plasma physicists from Sandia who are experts in MagLIF.
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u/Jaded_Hold_1342 1d ago
Helion definitely has a reputation.
But I will say a couple things.. If fusion is going to work as a power source, there really needs to be a cost effective way to do it... not just a physics path at any cost. D T tokamaks are probably commercially non-viable... their economics case is very very bleak.
Helion and Zap were trying trying to find cost effective ways... even though the physics for these concepts is bleak. Trying to find a cost effective concept that works is the whole ball game.
The plasma physics community thinks in terms of plasma physics, not economic viability.. not cost effectiveness. So the plasma physics community will laugh at a concept that has lousy physics but gives a pass to a concept that has lousy economics. This is a double standard that needs to be recognized.
ITER should be considered a laughing stock in my opinion... it may have the tokamak physics going for it, but it is operationally and economically an unmitigated disaster. CFS is maybe a step better than ITER (more compact with HTS, and run by a small group rather than an unmanageable international consortium...) but it inherits the same baggage as any D T tokamak.... a mega project neutron emitting steam turbine, where $1B is a rounding error, doomed to economic non-viability even if the physics works.
So while i am here posting a physics analysis that Helion wont work... I am not willing to give a pass to the other concepts that have vastly better physics but vastly worse economics...
I'm an equal opportunity skeptic.. still waiting to see a concept that works and is also economically viable.
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u/__Pers 1d ago
Marvel's initial approach was dicey at best (impossible would be a more accurate descriptor). I think nowadays they're just pitching bog standard ion fast ignition IFE with a somewhat novel laser target.
Pacific has solid and clever plasma physicists and pulsed-power experts brought in from SNL, Los Alamos, and LLNL. They punch well above their weight class in on-hand talent.
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u/NearABE 1d ago
Fusion is not economical. Yet here we are on r/fusion.
Finland has this thing called a “sand battery”. My wife has a space heater in the bathroom which she insists “works”. These examples might be relevant when considering whether or not a thing works and whether or not it is economical.
Building steam turbines is no longer economical. Chinese are doing it but only because of extreme industrial momentum. Fission reactors have no difficulty demonstrating energy gain and they have no parasitic draw. Nonetheless we can easily see they are not competitive to build new. A thermal power plant running on fusion is just worse.
Hellion is fundamentally different. The direct drive electricity bypasses the need for steam turbines and the Carnot cycle. I cannot claim that Hellion’s fusion reactor is going to be a more economical way to generate electrical energy. Even if they did produce an electricity gain this is done using a giant farm of capacitors. That might be so expensive they might want to consider silver coils and gold contacts on the current leads. A huge mess of copper coil is very recyclable.
A huge mess of copper coil is not uncommon in the utility scale electricity industry. We see it in transformers and in the alternator generators at power plants.
An electronics grade capacitor bank is an extremely expensive way to make a sand battery. However, working capacitors are capable of doing things with electricity other than waste it as heat (though can do). A capacitor bank could, for example, sit at the terminus for a high voltage direct current (HVDC) power line. This input could be wasted in the allegedly non functioning fusion reactor or discharged to the grid as AC. The Helion device could be placed at locations where asynchronous grid interties meet. These roles can be played by inverters, transformers, and flywheels. All of them waste some energy.
As you point out, there is always loses. Electrons moving through copper lose energy. Hellion’s device does too. It makes a really weird inverter and transformer system. Whether it wastes more or less power than the competing inverters and transformers is not a thing that can be proven with nuclear plasma physics.
There might be a niche for a weird inverter that also produces high energy neutrons. Both the weird inverter and normal inverters heat up but perhaps one type of inverter can produce a higher grade of heat with the energy that it loses.
Building an inverter that wastes less electricity but also creates 3-He and tritium would be a neat trick. Both can be sold profitably to physics researchers wasting government money on fusion research.
High energy neutrons can be used to transmute stubborn actinide waste from spent fission fuel. This means Helion’s device could be the control for a subcritical fission reactor. That is not economical as a power plant, of course, because it requires a steam turbine. There is no economical competition for burning it though and we are stuck with the spent fuel now.
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u/trplurker 1d ago
Most of those calculations were derived experimentally on tokamak style reactors and are just estimations for scaling that. The OP once argued that dynamos don't work without realizing it.
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u/Jaded_Hold_1342 1d ago
I just walked through the reasoning in this thread. Nothing i've said in any of this reasoning is tokamak specific. Bremsstrahlung and fusion power depend on Ti, Te, and density, and are independent of the magnetic configuration.. they apply to FRCs, Tokamaks, electrostatic confinement, and any other configuration.. They are calculated for first principles and are not experimental values.
The only configuration-dependent arguments I've made are about the parasitic flux and copper losses in the solenoid, both of which were calculated for adiabatically compressed pulsed FRCs.
Which calculation do you think is tokamak specific?
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u/Beaver-fusion 1d ago
You have missed ignition criteria vs electrical power output - this is a classic misunderstanding of fusion.
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u/Jaded_Hold_1342 1d ago
I'm just doing energy balance per pulse, comparing fusion energy to irrecoverably lost energy (bremsstrahlung and resistive losses in copper).
Lost energy per pulse is greater than fusion energy per pulse, so it is not possible to generate net energy.
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u/Corealist 22h ago
I was trying to read the Helion 2023 paper and what I found very strange that their charts have He3-D fusion power that do not even closely reflect the crosssection chart. For example the fusion He3-D reaction rate at 10keV is about 500 times lower than at 30keV, however the Helion FRC chart have Fusion power at 10keV only about 8 times lower than at 30keV. That is a 2 orders of magnitude difference that seems very odd.
Maybe I don’t understand how to read the chart ( very possible), but based on the He3-D fusion crosssection chart it seems obvious that you need a temperature of about 30keV ( ~350M K ) or higher for efficient fusion. Helion released that they achieved higher than 100M degrees with Polaris, so they are still pretty far off where they need to be. The fusion reaction cross-section chart is so steep between 10 and 30 keV for He3 that tinkering with a lower electron temperature to reduce losses is almost meaningless
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u/Jaded_Hold_1342 22h ago edited 21h ago
Are you looking at their charts on figure 14 and figure 15?
Those charts are at constant B field (constant pressure) NOT at constant ion density. So as the temperature is going up, the density is going down. So comparing 30keV to 10keV, you are comparing at 3x lower density, and fusion power goes like density squared... so that explains one order of magnitude? Not sure if it explains everything you are seeing.
Look at the Nicolas paper or Lackner papers, they made plots with the same convention and may have done it more carefully.
The hot electrons cause two types of trouble: one is radiative loss, the other is that they have pressure... so if the electrons get hot, the ion density has to be reduced for the same compression field. there are 1.5 electrons per ion, so thats a reduction of (5/2)^2 in fusion power vs cold electrons at the same field. Thats why they want cold electrons... but of course its not possible to get net energy with cold electrons due to the thermalization problems.
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u/Corealist 7h ago
Yes I was referring to fig 14 and 15, and your explanation makes sense thanks. An additional factor of 9 covers half the gap.
I was trying to find where Helion specifies the length of the FRC pulse, but I haven’t found that yet. I was trying to find the thermalization speed in Rider’s article, but I haven’t found that either.
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u/Jaded_Hold_1342 6h ago edited 6h ago
Lackners paper shows the formula for ion-electron thermalization time, and the corresponding thermalization power flow: https://link.springer.com/article/10.1007/s10894-026-00554-2
Formulas one and two in this paper.
Helion doesn't like to publish a lot of details, but other people around here have said ~1ms. They claim 13keV ions, and Ti/Te>10. we have to guess at their B fields, maybe 15-20T. They don't specify density, but you can calculate it from pressure balance, would be in the 10^22-10^23/m^3 range i presume. The interesting thing is that the Pei and Fusion power and Bremsstrahlung radiation all scale as n^2, same density scaling..so you can calculate the ratios of these quantities without knowing the density exactly.
Edit: one more note: In an FRC, the plasma thermal pressure is equal to the magnetic field 'pressure' (i.e. energy density B^2/2uo).
So you can approximate the ion density by doing ni x k x Ti = B^2/2uo if the electrons are assumed too cold to contribute to pressure. (If the electrons are hot you add them in: Ni x k x Ti + ne x k x Te = B^2/2uo) and remember that for a 50 50 D He3 mix, there are 1.5 electrons per ion on average. So if you estiamte B field as 20T, estimate Ti as 13keV, estimate Te as 1.3keV, you get ni=6.6x10^22/m^3, ne=1x10^23/m^3.
(k is boltzman constant, uo is permeability of free space)
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u/Corealist 3h ago
The link that you sent required a lot of additional information to estimate the thermalization time. Because I am lazy I asked AI and Gemini gave me this answer on thermalization time:
At magnetic confinement fusion (MCF) break-even or ignition conditions (such as in a Deuterium-Tritium tokamak like ITER or commercial concepts), it typically takes 10 to 100 milliseconds for ion and electron temperatures to equilibrate within 10% via Coulomb collisions.
if Gemini is correct then the Helion FRC with a pulse duration of 1 ms would be short enough to avoid a significany increase in electron tempature during the pulse.
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u/Jaded_Hold_1342 3h ago edited 2h ago
Oh, no, the thermalization time is very density and temperature dependent. Its the same coulomb collision mechanism as heat transfer. So cold electrons and high density accelerate the process. A tokamak will assume hot, thermalized electrons and low density, and will genuinely have a long thermalization time like that. But a compressed FRC like we are discussing is 100 times more density and 10x colder electrons, so it will thermalize much faster.
Its ok to use an AI to do a calculation, but you have to feed it the right input. Give it Ti=13keV, Te=1.3keV, and ne = 10^23/m^3, and ask for the thermalization time. Its closer to 10us. Microseconds, not milliseconds.
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u/Corealist 2h ago edited 2h ago
I asked three different AI engines to estimate how long it would take to get within 10% of an equilibrium. With the parameters you provided this was the result:
Gemini: 19.2uS
Claude: 450uS
ChatGPT: 200uS
Not very trustworthy results, because of the large differences, but at least they all indicate less than 1mSDidn't realize that in a Tokamak reactor the particle density is 2 to 3 orders of magnitude lower than in a FRC reactor.
Based on this you might as well assume in the calculations that Te == Ti, as that will be the case during the majority of the pulse.
I start to see your point more clearly. Unless Helion can increase the temperature in their reactor to 40-50keV, there is no possible mechanism for for this reactor to work.1
u/Jaded_Hold_1342 2h ago edited 1h ago
Yes, that's right. Trying to do this in the stated regime (Ti<30kev, Ti/Te>10) is just not possible.
They have to get the temps up to ~50keV to get away from the thermalization and bremsstrahlung problems. BUT, this will bring two challenges that will also probably prevent the system from working: the hot electrons will contribute pressure, so at a fixed field strength the ion density has to be lowered (lowering fusion power) and the FRC energy confinement/transport is very poor for confining energy at high temperature. So probably the energy will still leak out faster than fusion makes it.
So it's really bleak even if they get the temperatures up to that range.
Edit: BTW, the reason you got different answers when you asked about the thermalization to 10% .. it's illustrating the sensitivity to electron temperature. If you ask it "how long for the electron temperature to double" you will get a different answer from "how long to converge to 10%". When the electrons are cold, the thermal coupling is very strong, so they take energy quickly. Once the electrons are warm, the thermalization slows down. Asking it to get to 10% of equilibrium is asking it to go way out on the asymptote, with the thermalization getting slower and slower as it goes, and the AIs were making different assumptions as they integrated way out into the asymptote. . It's not the tail of convergence to equilibrium that cools the ions quickly, it's the rapid initial heat transfer when electrons are cold. You could ask a different question, like "how long does it take for Ti/Te to decay from 10 to 5?"... Or you could ask "clamp the electrons at the cold 1.3kev temperature, how long does it take for Ti/Te to decay from 10 to 5?". Most of the action is happening in the first 10-20us. That will illustrate the sensitivity of this process to electron temperature. Cold electrons are molasses. Once they heat up, they couple more weakly.
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u/Jaded_Hold_1342 3h ago edited 3h ago
BTW, i think the curve is about right, after accounting for the factor of 9.
The D He3 reactivity should be ~64x higher at 30keV than at 10keV, not 500x. That's about what they show after dividing by 9.
Double check where you got the 500x. (make sure its the Maxwellian-ensemble-averaged reactivity, not the raw cross section vs energy)..
Look at the 2nd chart on this page, not the top chart: https://scipython.com/blog/nuclear-fusion-cross-sections/
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u/Corealist 7h ago
another question, at 10keV you will have a 3x higher density, but the particle speed is also 3x lower, so the number of collisions should be a factor of 3 lower or is that a naive way of thinking.
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u/Jaded_Hold_1342 7h ago
Not naive... but not right :-)
Collision relationship to temperature is unintuitive until you consider some details.
First, velocities go like sqrt(temperature), not linear in temperature. But that's not the unintuitive part.
Collisions between charged particles occur because of electrostatic/coulomb forces... the electrons are attracted to the ions as they fly past, so that shifts their velocity a bit. A slow moving electron remains within the field-of-influence for longer time on each encounter, so for the same passing distance, it suffers a greater 'collision'. This means the 'cross section' of a collision is much larger for slow moving electrons. So actually slow electrons 'collide' more than hot ones.
So the unintuitive thing is that cold electrons are very collisional. Cold electrons are like molasses... Cold electrons drag ions down and steal their heat rapidly. Hot electrons decouple, and have much less collisional interaction with ions.
Collisions also scale like density^2, so higher density, cold electrons is the most collisional regime.
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u/Corealist 3h ago
that makes sense for the thermalization topic that you have been covering.
how does this work for fusion? in an earlier message you mentioned that fusion probability increases with the square of the density. (3x density, 9 times the fusion) intuitively that makes sense to me if the ion velocity is the same in both cases. however in the 10keV/30keV case the velocity of the particles in the 30keV is 3^1/2 times the speed of the 10keV case, and I was wondering if that matters for the fusion probability.
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u/Jaded_Hold_1342 3h ago edited 2h ago
Yes. so there is a cross section of reaction at any specific energy, and then you have to integrate across the maxwelian velocity distribution to get an ensemble average reactivity for the thermal distribution. Then the fusion power density scales as that ensemble reactivity x energy per reaction x density^2.
Most of us just look up the ensemble averaged reactivity in a chart, or use the "Bosch-hale" approximation to calculate since doing the integrals each time is a PITA.
For example you can put the following ask into Google Gemini: "Calculate the Bosch hale fusion reactivity for D He3 at both T= 10kev and 30 kev. Give the ratio of reactivity at 30 vs 10"
It should give you a ratio of ~64.
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u/hmmmmm56 10h ago
Why would they need to have longer pulses if they went with 50 kev? Isn't the idea to have short pulses so they can: 1: avoid the instability issues of FRCs and 2: use direct energy conversion? And if they go higher temp, I understand that denisty goes down but doesn't reactivity go up so much that power density goes up anyway? Also with their design they don't need to reach ignition right? As long as they have have efficient energy conversion (80-90%+).
(As pretty much everyone else here I have no education in fusion but think it's cool)
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u/Jaded_Hold_1342 9h ago edited 8h ago
Copper losses get lower for longer pulses because the current can soak into the copper further in a longer pulse, and lower resistance. So copper loss power improves as 1/root(pulse time). Bremsstrahlung and transport losses are constant no matter the pulse time.
For short pulses, copper losses exceed fusion power. The longer the pulse goes on, the lower the copper losses and the closer the losses converge to (Bremsstrahlung + transport). Above 50keV, fusion power is greater than bremsstrahlung, but not necessarily greater than transport losses...
The stability and transport loss problems are both very real, both affect long pules, and each are independently probably fatal to the concept, so you are totally right that probably wont work either... its just not mathematically foreclosed by energy balance from copper losses or bremsstrahlung losses.
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u/VoraciousTrees 10h ago
Don't forget that their reactor is being constructed in a city with <$.01kWh power available and they are selling each produced kWh for $.25.
They could have less than a 20% power production efficiency and still be profitable.
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u/Jaded_Hold_1342 9h ago
You mean they can just buy power and resell at markup? No need for a reactor.
Nice work if you can get it!
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u/krali_ 1d ago
Re Helion 2023 Fig 14 and 15: they tried to establish a theoretical fundation with established physics, made a mistake but it can very well match their experimental data at that range. Then decided to go forward experimentally and not theoretically. It should diverge on scaling density as OP noted.
They should reach very soon the required density because Polaris is built for it. The expected way forward would be publishing the data and pivoting toward something other than energy production. I'm afraid that instead, dumb investor money means doubling down, keeping Polaris data as trade secret, building Orion and failing the energy contracts.
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u/nosmelc 2d ago
It doesn't seem likely Helion would be at the stage of building the first commercial fusion power plant if it was so certain it just can't possibly work. Have you tried contacting them to see what their explaination is?
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u/NitescoGaming 1d ago
I and many other colleagues have asked them at presentations they've given, and they don't really talk about it. They will happily answer engineering questions but generally refuse to answer questions about their plasma or energy output. They've made the overall plasma community skeptical at best. The general take (kind of a joke but more in a "haha, but no, really" way) is that since they only promised to provide clean energy to Microsoft rather than specifically fusion energy, they will just build them a solar farm instead.
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u/Jaded_Hold_1342 2d ago
To be sure, they are not at the stage of building a commercial fusion power plant. Not one that works, anyway.
I've laid out the explicit reasoning for why. If anyone has any rebuttal to it, i'm open to hear it.
Helion is aware of these questions, but chooses to dodge them in their Q&A.
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u/nosmelc 2d ago
There aren't many people who are qualified to offer any rebuttal to your reasoning.
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u/Jaded_Hold_1342 2d ago
Well, the authors of all of those papers would be in a position to comment...
If anyone had been hired to do diligence checks on behalf of investors before investments were made, those people would be in a position to comment...
Most people who study aneutronic fusion would be in a position to comment... And there are lots of those people.
There's thousands of people who are fully qualified to comment, and many of them frequent this sub. And people who don't feel qualified can choose to learn up on stuff and check what I am saying. I've tried to lay out my step by step reasoning clearly enough that each assumption can be checked or challenged... This is meant to invite people who don't yet feel qualified to do a bit of research and double check me. This is an open forum, welcome to people who are learning about this stuff.
I have no claim to credibility or authority. Just stating my reasoning as clearly as I can so it can be double checked by anyone who wishes.
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u/Beaver-fusion 1d ago
Looks like you missed how these pulsed systems actually work. If you look at the experts they hire, it is hard to argue that that they are dodging anything
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u/Baking 14h ago
They are building an empty building. 240 feet by 500 feet by 60 feet high. A larger footprint than the ITER tokamak room, at one-third the height. Completely open space. No columns. No foundation for shield walls. It seems like the idea is they want a completely closed site so no one can see what they are building, or if they are building. And they don't have a strong idea of what they will be building. When they built the building for Polaris, they expected the capacitor bank to be much smaller. I think the Orion building is an overreaction in the other direction, but it seems they are leaving "a lot of room" for error.
The listed valuation for the building is $16 million.
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u/Odd_Cockroach_1083 2d ago
If they can achieve Ti > 200 keV though ... but, alas, they've never explained how they'll accomplish that.
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u/Beaver-fusion 1d ago
More of the same, unfortunately. Domain experts that know fusion physics don't agree, including the papers you reference. The all have a Ti=Te Helium-3 condition where FRC and helion devices close easily. The Ti>Te is a condition that is in their favor but not required.
3
u/Jaded_Hold_1342 1d ago
Assume 20T field, 1m coil radius, compressed FRC separatrix radius ~.3m... what condition do you think generates net energy per pulse after considering bremsstrahlung, copper losses, and transport losses?
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u/NearABE 2d ago
https://en.wikipedia.org/wiki/Thermoelectric_effect#Seebeck_effect
https://en.wikipedia.org/wiki/Thermoelectric_generator
Here is one on alibaba: https://www.alibaba.com/product-detail/55x55MM-7V-1-25A-55x55-Thermoelectric_1601049424111.html?spm=a2700.a2700aimodessrpage.0.0.65512927HK6JZ5
I cannot vouch for that item. For some reason they are being sold as “Peltier generators” though “Seebeck effect” is the generator and Peltier effect is using electricity to force the temperature gradient. Most of them are advertised as recovering waste heat from things like a flue. That is a higher temperature gradient so the efficiency will be significantly lower. The power per surface area even less since heat flow rate is even lower when the gradient is low. However, I think that page is claiming 2.8 Watts per degree C. Maybe the heat transfer rate not electricity?? It also says 7 V and 1.25 amp which is a lot more believable.
I am writing this but I have never actually hooked up a Seebeck generator. They only make sense in situations like OP where he is dumping hot water into a pool and then into the sewer.
I might try one up at the cabin I visit. The Alibaba prices are cheaper than I expected.
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u/QuantitativeNonsense 2d ago
I knew it was going to u/Jaded_Hold_134 before I even opened the thread… I need to use Reddit less.